Expose the previously private KID field of the Client type. This allows callers which have locally cached their key identity to avoid needing to make a call to the ACME service every time they construct a new client. Fixes golang/go#46303 Change-Id: I219167c5b941f56a2028c4bc253ff56386845549 Reviewed-on: https://go-review.googlesource.com/c/crypto/+/354697 Trust: Katie Hockman <katie@golang.org> Reviewed-by: Katie Hockman <katie@golang.org> Trust: Roland Shoemaker <roland@golang.org> Run-TryBot: Roland Shoemaker <roland@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org>